She married fellow Labour MP Nick Smith in July 2014.[4] She has two children from a previous relationship.

Chapman worked as constituency office manager for Darlington Labour MP Alan Milburn. After a career break for children, she returned to politics at Darlington Borough Council when she was elected as borough councillor for the Cockerton West ward in 2007.[5]

In November 2009, Chapman was shortlisted as one of four candidates to succeed Milburn as Labour's parliamentary candidate for Darlington on an open shortlist.[5] She was selected to stand for parliament by the local constituency party the following month. Chapman said: "This shows that the people of Darlington want to choose a Darlington person who will put the town first."[6] She was elected Darlington MP in the 2010 general election with a majority of 3,388.[7] As a result of her election victory, she decided to stand down as a councillor.[8]

In 2011, Chapman was appointed as Shadow Prisons Minister.[10] She had previously written policy recommendations on the subject of incarceration including a recommendation that prison officers should receive training to help them rehabilitate inmates.[10]

Chapman became the Shadow Minister for Childcare and Early Years in January 2016, but resigned in the summer of the same year among dozens of Labour frontbench colleagues.[11] She has since rejoined the shadow frontbench as Shadow Minister for Exiting the European Union[12] alongside Keir Starmer. The department was set up as a consequence of Britain voting leave during the United Kingdom European Union membership referendum, 2016 on 23 June 2016.